There is a reason to believe that the lung is a hormone responsive organ, but, to date, there is certainty in a direct effect on the lung of only one type of hormone, the glucocortoids. We propose to demonstrate that pulmonary function is ultimately regulated by a number of hormones, and that these hormones elicit a defined biological effect on the lung by interacting directly with subcellular components of the organ. Observations will be made on hormonal effects on surfactant production, collagen synthesis, glucose utilization, and RNA, DNA, and total protein biosynthesis in the rat lung, using both lung slices incubated in vitro and isolated, perfused lung preparations. These will be related to studies on the detection, characterization, and quantification of specific hormone receptors in subcellular components of the rat lung. The effects of induced hormonal imbalances and of oxygen toxicity on biochemical parameters and hormone receptor concentrations in the lung will be examined. In addition, a radioimmunoassay for rat lung surfactant will be developed, so as to provide a sensitive, rapid, and simple means of assessing hormone effects on surfactant production.